What Are the Side Effects of Metoprolol Tartrate?

Metoprolol tartrate, the immediate-release form of one of the most widely prescribed beta-blockers, commonly causes fatigue, dizziness, and a slower-than-usual heart rate. Those three account for the majority of complaints, but the drug’s reach extends further than most people expect. Because metoprolol is fat-soluble enough to cross into the brain, it can disrupt sleep, trigger vivid nightmares, and contribute to mood changes. It also nudges metabolism in unfavorable directions for some people and can make exercise feel harder than it should. The severity of these effects varies enormously from person to person, and a surprising amount of that variation traces back to genetics and drug interactions rather than dose alone.

Fatigue, Dizziness, and a Slower Heart Rate

The side effects you are most likely to notice first are fatigue and lightheadedness. Both stem directly from what the drug is designed to do: slow the heart and lower blood pressure. With less cardiac output reaching your muscles and brain at any given moment, you may feel sluggish during the day or briefly dizzy when you stand up quickly. These effects tend to be most pronounced during the first week or two, before your body adjusts.

Bradycardia, a resting heart rate that dips lower than normal, is the cardiovascular side effect that gets the most clinical attention. In a study comparing groups of patients with different abilities to metabolize metoprolol, roughly one in four normal metabolizers developed bradycardia, while the rate climbed to about two in five among those who broke the drug down slowly.¹ For most people a mildly slow pulse is harmless, but if your resting rate drops into the low 50s or below and you feel faint or short of breath, that warrants a conversation with your prescriber about dose adjustment.

Nightmares, Vivid Dreams, and Sleep Disruption

One of the stranger effects of metoprolol tartrate is its ability to hijack your sleep. Because the drug is lipophilic, meaning it dissolves easily in fat, it crosses the blood-brain barrier more readily than water-soluble beta-blockers like atenolol. Once in the central nervous system, it appears to interfere with REM sleep, alter noradrenergic signaling, and suppress melatonin production, a combination that can generate intensely vivid or disturbing dreams.²

The melatonin link is particularly telling. When researchers measured overnight melatonin excretion in patients who developed nightmares on beta-blockers and compared them to matched patients on the same drugs who slept fine, every single patient with nightmares had lower melatonin levels than the controls.³ This suggests that some people are predisposed to these central nervous system effects, and the melatonin suppression may be the mediating pathway. If you start having nightly nightmares soon after beginning metoprolol, that is not a coincidence and it is not something you need to tough out. Switching to a less lipophilic beta-blocker or adjusting timing often resolves the issue.

Beyond nightmares, case reports describe confusion, visual hallucinations, delirium, gait problems, and general cognitive fogginess, especially in older adults.⁴ These neuropsychiatric reactions are relatively uncommon and more often seen at higher doses or in overdose situations, though non-dose-dependent cases have been documented as well.⁵ The key point is that mental and emotional changes on metoprolol are a recognized pharmacological effect, not “just stress.”

Weight Gain and Metabolic Effects

Weight gain on metoprolol tartrate is real and measurable, not dramatic, but persistent enough to frustrate people already managing conditions like diabetes or obesity. In the GEMINI trial, which compared metoprolol tartrate against carvedilol in patients with diabetes and high blood pressure, those on metoprolol gained an average of about 1.2 kg over the study period, while those on carvedilol gained essentially nothing.⁶ The gap widened as body mass index increased: people who were already obese gained significantly more on metoprolol than on carvedilol, and those in the morbidly obese range saw a difference of nearly 2 kg between the two drugs.

The metabolic picture goes beyond weight. Metoprolol has been shown to decrease insulin sensitivity and increase markers of oxidative stress in patients with metabolic syndrome, effects not seen with newer vasodilating beta-blockers like nebivolol.⁷ That said, the degree to which metoprolol truly causes insulin resistance in the broader population is debated. An earlier study in hypertensive subjects found that while the calculated insulin sensitivity index dropped during metoprolol treatment, the actual glucose infusion rate didn’t change significantly, leading the researchers to suggest the apparent insulin resistance may partly reflect how the drug alters insulin clearance rather than a genuine worsening of the body’s response to insulin.⁸

For people with diabetes, there is an additional concern: beta-blockers can mask the typical warning signs of low blood sugar, especially the rapid heartbeat and tremor that normally prompt you to eat something. Research on metoprolol specifically found that it did not worsen prolonged low blood sugar episodes in insulin-dependent diabetics, and it actually increased sweating (which can serve as an alternative warning sign), but other common symptoms like racing heart were blunted.⁸ If you use insulin, your doctor has probably mentioned this, but it is worth flagging again: your body’s alarm system for low blood sugar may be quieter than usual on this medication.

Exercise Feels Harder

If you have ever felt like your legs turned to concrete after starting metoprolol, the pharmacology backs you up. Beta-blockers cap your heart rate during exercise, which limits the amount of blood (and oxygen) your muscles receive when they need it most. In a study measuring exercise performance during beta-blocker therapy, perceived exertion increased during exercise and total endurance dropped by about 15%.⁹

The effect is dose-dependent. At lower intravenous doses of metoprolol, peak exercise heart rate dropped substantially, from around 189 to 155 beats per minute in healthy subjects. At higher doses and during chronic treatment, the ceiling came down even further, and maximal oxygen uptake, exercise time, and circulating fuel sources like blood sugar and free fatty acids all declined.¹⁰ This does not mean you should stop exercising on metoprolol. It means your target heart rate zones from before the medication no longer apply, and you should expect a lower ceiling on how hard you can push. Moderate, steady-state exercise is generally well tolerated; high-intensity intervals are where you are most likely to hit the wall.

Sexual Side Effects and the Power of Expectation

Erectile dysfunction is one of the most feared side effects of beta-blockers, and it is commonly listed in patient information sheets. But the reality is more complicated than “metoprolol causes ED.” A telling study randomly assigned men with high blood pressure to take metoprolol under three conditions: some were told which drug they were receiving, some were told they were taking a beta-blocker without being told it could affect sexual function, and some were not told what the drug was at all. The rate of erectile dysfunction tracked almost perfectly with how much the men expected it to happen. When researchers tried treating the ED with either a placebo pill or tadalafil (Cialis), both worked equally well, because the dysfunction was largely psychological in origin.¹¹

This does not mean every case of sexual dysfunction on metoprolol is imaginary. Beta-blockers can reduce cardiac output and potentially affect blood flow to peripheral tissues. But the evidence suggests that expectation and anxiety play a much larger role than the pharmacology, at least for erectile dysfunction specifically. If you have noticed changes in sexual function after starting metoprolol, it is worth discussing with your doctor before assuming the drug is the sole culprit, because the fix may be simpler than switching medications.

Why Side Effects Hit Some People Harder

One of the most important and underappreciated factors in how metoprolol affects you is how quickly your liver breaks the drug down. Most of metoprolol’s metabolism runs through a single liver enzyme called CYP2D6, and genetic variation in the gene that codes for that enzyme is remarkably common. Roughly 5 to 10 percent of people of European descent are “poor metabolizers,” meaning they have little or no CYP2D6 activity. In these individuals, a standard dose of metoprolol produces blood levels several times higher than intended, essentially turning a moderate dose into an overdose.

The clinical consequences are measurable. In a study comparing outcomes across metabolizer groups, poor metabolizers had a bradycardia rate of about 41%, compared to 25% in normal metabolizers, and the odds of developing bradycardia were roughly 60% higher in the poor metabolizer group.¹ Dutch pharmacogenomics guidelines now recommend slower dose titration and lower maintenance doses for people known to be poor metabolizers.

You do not need a genetic test to encounter this problem, though. Certain common medications can effectively turn a normal metabolizer into a poor one by blocking CYP2D6. The most clinically significant culprits are the antidepressants paroxetine (Paxil) and fluoxetine (Prozac). A systematic review found that paroxetine increased metoprolol exposure by three to five times and significantly lowered both heart rate and blood pressure, with case reports of outright bradycardia and heart block resulting from the combination.¹² If you are prescribed both metoprolol and one of these antidepressants, your prescriber should be aware of this interaction, but in practice it is missed more often than it should be. Mentioning all your medications, including over-the-counter ones, at every appointment matters here.

Older Adults Face Extra Risks

Age compounds nearly every side effect on this list. The body’s ability to clear drugs slows with age, raising effective blood levels even at unchanged doses. Reflexes that normally compensate for blood pressure drops, such as the baroreceptor response that keeps you from feeling faint when you stand, become sluggish. The result is that older adults on metoprolol are more prone to orthostatic hypotension, the sudden lightheadedness or near-blackout that happens when you go from sitting to standing. Orthostatic hypotension already affects anywhere from 5 to 33% of elderly individuals, and antihypertensive drugs including beta-blockers make this problem considerably worse.¹³

Falls are the downstream danger. A dizzy spell that a 40-year-old shakes off can send an 80-year-old to the emergency room with a hip fracture. The central nervous system effects discussed earlier, confusion, cognitive slowing, gait problems, are also more common in older adults and can compound the fall risk. One case report detailed an 84-year-old man who developed confusion, fatigue, lightheadedness, nightmares, and balance problems over the course of four weeks on metoprolol.⁴ These symptoms were initially attributed to aging or dementia before the medication connection was made. If an older family member has recently started or increased metoprolol and seems “not quite right,” the drug deserves a hard look before more serious diagnostic workups begin.

Stopping Suddenly Can Be Dangerous

Metoprolol tartrate should never be stopped abruptly. When you take a beta-blocker regularly, your body upregulates its beta-adrenergic receptors to compensate for the blockade, essentially becoming more sensitive to adrenaline. If you suddenly remove the blocker, all that heightened sensitivity is unmasked at once. Research has documented a roughly 52% rebound increase in cardiac sensitivity to stimulation and a 15% rebound rise in resting heart rate within two to eight days of metoprolol withdrawal.¹⁴

For someone using metoprolol solely for high blood pressure, this rebound can feel like intense palpitations, anxiety, and a spike in blood pressure. For someone with underlying coronary artery disease, the consequences can be far more serious. Abrupt withdrawal has been linked to unstable angina and even heart attacks, driven by an overshoot in heart rate that increases the heart’s oxygen demand beyond what narrowed arteries can supply.¹⁵ The standard recommendation is to taper the dose over one to two weeks under medical supervision. If you run out of pills unexpectedly, contact your pharmacy or doctor rather than simply going without.

Tartrate Versus Succinate and Why It Matters for Side Effects

Metoprolol comes in two salt forms: tartrate (the immediate-release version, typically taken twice daily) and succinate (the extended-release version, taken once daily). They contain the same active molecule, but their side-effect profiles differ because of how they deliver it. The tartrate form produces a sharp peak in blood levels after each dose, followed by a trough before the next one. The extended-release formulation smooths out this curve, producing lower peak concentrations and more consistent drug levels throughout the day.¹⁶

In practical terms, this means tartrate users are more likely to experience side effects that track with peak levels, things like pronounced dizziness or fatigue an hour or two after each dose, followed by a return of symptoms the drug is meant to control (palpitations, blood pressure elevation) as levels drop before the next dose. The succinate form avoids those extremes. If your side effects clearly follow a pattern of “worse after taking the pill, better hours later,” the timing profile of the tartrate form may be the issue, and switching to once-daily succinate could help without changing the overall drug.

Cold Hands and Peripheral Circulation

A widespread belief among patients and even some clinicians is that beta-blockers reliably worsen cold extremities, especially in people with Raynaud’s phenomenon. The mechanism is plausible: by blocking beta-2 receptors in peripheral blood vessels, the drug could tip the balance toward vasoconstriction. However, the evidence for metoprolol specifically is weaker than the reputation. A controlled study comparing propranolol, metoprolol, and pindolol found no significant effect on finger skin perfusion or recovery after cold challenge for any of the beta-blockers tested, in either Raynaud’s patients or those with hypertension, when compared to placebo after a single dose.¹⁷ This does not mean no one ever gets cold fingers on metoprolol, but it does suggest the effect is less universal and less pharmacologically straightforward than often assumed. If your extremities feel genuinely cold and painful, the symptom is worth mentioning, but do not assume it is automatically the beta-blocker’s fault without exploring other causes.

1
PubMed Central. Metoprolol and CYP2D6: A Retrospective Cohort Study Evaluating Genotype-Based Outcomes
2
PubMed Central. Vivid Dreams and Nightmares as an Adverse Effect of Beta-Blockers in the Treatment of Episodic Migraine
3
PubMed. Depressed melatonin secretion in patients with nightmares due to beta-adrenoceptor blocking drugs
4
PubMed Central. Metoprolol-Associated Central Nervous System Complications
5
General Hospital Psychiatry. Sleep disorders, nightmares, depression and anxiety in an elderly patient treated with low-dose metoprolol
6
PubMed. Body weight changes with beta-blocker use: results from GEMINI
7
PubMed Central. Differential effects of nebivolol and metoprolol on insulin sensitivity and plasminogen activator inhibitor in the metabolic syndrome
8
PubMed. The effect of metoprolol treatment on insulin sensitivity and diurnal plasma hormone levels in hypertensive subjects
9
PubMed Central. The effect of beta-adrenoceptor blockade on factors affecting exercise tolerance in normal man
10
PubMed. Effects of acute and chronic metoprolol administration during submaximal and maximal exercise
11
PubMed. Erectile dysfunction after therapy with metoprolol: the Hawthorne effect
12
PubMed Central. The impact of CYP2D6 mediated drug–drug interaction: a systematic review on a combination of metoprolol and paroxetine/fluoxetine
13
PubMed. Drug-induced orthostatic hypotension in the elderly: avoiding its onset
14
PubMed. Metoprolol withdrawal phenomena: mechanism and prevention
15
The American Journal of Cardiology. Beta-adrenergic blocker withdrawal
16
PubMed. Pharmacokinetic and pharmacodynamic properties of a new controlled-release formulation of metoprolol: a comparison with conventional tablets
17
PubMed Central. The influence of different beta-blocking drugs on the peripheral circulation in Raynaud’s phenomenon and in hypertension